OFRU Recycling GmbH Co KG Babenhausen Germany

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The Swiss coating manufacturer Karl Bubenhofer AG was planning to acquire various wash plants for cleaning batch, mixing and multi-trip containers efficiently. The contaminated solvents obtained during the wash process were then to be treated automatically by distillation. The distillation plant had to have a suitable output, operate continuously and be simple to operate. Another requirement was the ability to combine this plant with the wash plants in a new building complex. A distillation plant suitable for this purpose was supplied by OFRU Recycling in Babenhausen/Germany.

Karl Bubenhofer AG, known by the name, "Kabe-Farben", is regarded as one of the largest paint and coating producers in Switzerland and has been producing coating materials since 1926. The product range covers architectural paints and plasters, powder coatings and industrial liquid paints. The company's wide range of customers includes industrial, commercial and contract paint companies as well as resellers at home at abroad.

Kabe offers a special service in cooperation with regional painters' associations. For a small charge customers and painters can offload their waste paints and contaminated solvents to Kabe in special multi-trip containers. About 160 tonnes per year of spent solvents

Distillation Plant Material Removal
Figure 22.3.1. Soiled multi-trip container.

are obtained by way of this disposal system. Even before the planning phase, these contaminated spent solvents were treated with the company's own small distillation plant.

Until now, manual cleaning of these multi-trip containers and large batching and mixing vessels from production was particularly inconvenient and labor-intensive for Kabe. A wash plant for mobile large containers (250-1800 l volume) and for small drums pails (about 80-100 per day) would obviate the unpleasant manual cleaning task in the future. A combination of container wash following by distillation therefore seemed very practicable. The treated clean solvent would feed the wash plants and ensure thorough cleaning. The company was also interested in further processing a part of the distillate for Kabe products.

When the solvent requirement of the container wash plant and the customers's spent solvent quantities were added together, the total was about 200 tonnes of contaminated solvents per year. Solvents such as toluene, ketones, esters, ethyl acetate, xylene, glycol and petroleum spirits were to be separated almost completely from solids such as alkyd, 2-pack, epoxy and polyester resins.

The solvent recovery plant had to meet the following requirements:

  1. Combination with wash plants and storage tanks
  2. Distillation with a high rate of recovery
  3. Continuous operation (24 hour)
  4. Distillation output of 200-400 l/h
  5. Low maintenance
  6. Minimum operating and control times
  7. Residue to be contaminated only slightly with residual solvent

Kabe-Farben found the solution Rio Beer, a wash plant producer from Switzerland.

Rio Beer supplied not only the wash plant design but also integrated OFRU Recycling from Babenhausen in Germany with its solvent recovery plants. OFRU Recycling provided the necessary expertise from the paints and coatings sector.

Kabe-Farben visited the OFRU pilot plant in Babenhausen and was able to recover 224 kg of clean solvent within a few hours from 300 kg of contaminated solvent. A quantity of 76 kg of solid paint slurry was then discharged from the distillation unit. An analysis afterwards showed that the residue contained only 5.5% solvent. More than 74% of the solvent could therefore be recovered in the first instance.

The solution

Kabe decided in favor of a vacuum evaporator with an integrated stirrer. The ASC-200 model together with three solvent tanks stand together in an explosion-proofroom. The cus-

Ofru Recycling Asc 100
Figure 22.3.2. Solvent circuit and treatment.

tomer's contaminated spent solvents are poured in through a large sieve by means of a drum tilting device. Twin diaphragm pumps then convey the contaminated solvent to the first soiled solvent tank. In view of the large proportion of paint in the solvent (5-20 vol.%), the solvent is kept homogeneously in motion in the tank by means of the stirrer. Another soiled solvent tank is connected up to the wash circuit and supplies the solvent for pre-washing.

The ASC-200 model used by Kabe operates entirely under vacuum. A considerable increase in capacity is achieved by means of the vacuum equipment; moreover, distillation is milder and residue is largely solvent free.

The contaminated product is introduced automatically by suction into the evaporator by means of a magnetic valve and the vacuum until it reaches the height of a capacitive level controller, which keeps the solvent level constant during continuous opera-Hgure 22.3.3. Wash pkiit foi- imxmg w^ek. tion. The filling operation is adjusted in such a way that no excessive cooling or interruption in the distillation process takes place.

The solvent is usually heated by means of a double jacket with its own thermal oil facility. Kabe, on the other hand, operates a catalytic waste air purification plant. The solvent-air mixture obtained in the plant is converted catalytically to heat and stored as an energy store. A small portion of the heat thereby obtained is absorbed in our case by a thermal oil system and released to the distillation plant.

A stirrer is fitted inside the ASC-200 distillation plant. Its scrapers rotate inside the inner wall of the vessel. They keep the heat transfer surface free from encrustation and guarantee uniform heat transfer into the boiling solvent. The stirrer keeps the liquid in motion

Figure 22.3.4. ASC-200 distillation plant in the explosion-proof room.

Figure 22.3.5. Residue transferred to PE pail.

Figure 22.3.4. ASC-200 distillation plant in the explosion-proof room.

Figure 22.3.5. Residue transferred to PE pail.

and thereby promotes evaporation of the solvent. Finally, the solvent vapor reaches a water-cooler tubular condenser provided with a cooling water control unit. The condensed, clean distillate is pumped from here to the distillate tank. This tank has a level control and now feeds the clean solvent directly into the wash plant for a second wash. The distillation process takes place fully automatically and lasts about 2 days. Distillation of the bottom product takes place independently afterwards. After the residue has been thickened to a predetermined viscosity, the equipment shuts down automatically. The still is drained by means of a discharge valve at the bottom of the cone. The 200-300 kg of compact greyish residues are transferred to 20 completely empty 20 liter plastic pails and then fed to an inexpensive solid waste incineration process. No further cleaning operations are required at the plant so the stirred distillation unit is ready for use again immediately.

The plant used at Kabe treats about 200 liters of solvent per hour. At about 200 tonnes per year it is therefore being used to 60-70% of its capacity at present. Since its installation, the distillation plant has been operating for 5 days per week with very little maintenance. A few mechanics maintain the plant twice a year without external support.

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